The present invention relates to a charge-coupled device (CCD) type color video camera, and more particularly to a video signal processor for a single-plate color filter array (CFA) CCD type color video camera.
In a general CCD type color video camera as shown in FIG. 1, a video signal processor is provided for converting a CCD output signal into a television signal having a luminance signal and color difference signals and output the television signal. A conventional video signal processor comprises a delay circuit 10 which receives a CCD output, signal and outputs a 1H line delay signal and a 2H line delay signal ("H" representing one period of the horizontal synchronizing signal), a luminance signal processor 12 which receives the CCD output signal and the 1H and 2H line delay signals and outputs a luminance signal (Y), and a chrominance signal processor 14 which also receives the CCD output signal and the 1H and 2H line delay signals to output a color difference signal (C).
Luminance signal processor 12 comprises vertical aperture processor 12a which receives the CCD output signal and the 1H and 2H line delay signals and performs vertical aperture processing, a horizontal aperture processor 12b which receives only the 1H line delay signal and performs horizontal aperture processing, an adder 12c which adds the output signals of the vertical and horizontal aperture means and the 1H-delayed CCD output signal, and a first gamma (.gamma.) correction circuit 12d which gamma-corrects the output signal of the adder and outputs a final luminance signal.
Chrominance signal processor 14 comprises an RGB matrix circuit 14a for receiving the CCD output signal and the 1H and 2H line delay signals and outputting R, G and B color signals, second, third and fourth gamma correcting circuits 14b, 14c and 14d for performing gamma correction with respect to the RGB color signal from RGB matrix circuit 14a, and an encoder 14e for receiving the three gamma-corrected primary colors (R, G and B) so as to output the color difference signals R-Y and B-Y as part of the composite video signal for a color television. A single plate CFA-CCD may obtain the color separation and the high-resolution luminance signal according to the color arrangement characteristic of the color filter array by generating CCD output signals, so as to repeatedly apply S1 (R+G+2B) and S2 (R+2G) to the 1H line and S1 (2G+B) and S2 (2R+G+B) to the 2H line, respectively. Accordingly, even when a subject producing two equal luminance signals is to be displayed, since the RGB composition ratios of S1 and S2 are different from each other, the difference between the signal levels of S1 and S2 occurs. For example, if the colors of the displayed object are blue, the 1H line has S1 (2B) and S2 (0) and the 2H line has S1 and S2 (both equaling B) so that DC levels are equal at both lines, but the 1H line is repeatedly provided with 2B and 0 so that the 2H line is repeatedly provided with the values B and B, i.e., DC components. Therefore, the conventional circuit composition shown in FIG. 1 would be affected by a horizontal noise component which is generated on the screen due to a fluctuation in the DC level after gamma compensation, which degrades picture quality. That is, as shown in FIG. 2, gamma compensation circuit 12d exhibits a non-linear gamma-compensating characteristic curve, so that the 2H line has S1 and S2 (both equaling B) thereby the B-input DC level is gamma-compensated into the output DC level at position "a," and "b" is the gamma characteristic of the input value 2B. However, the 1H line has S1 (2B) and S2 (0), thus the repeatedly input DC level is shown as 0 and 2B respectively, so that the output DC level at position "c" as an average of "0" and "b" is obtained regardless of gamma compensation. Therefore, upon the completion of the gamma compensation, the DC levels of the 1H and 2H lines differ by as much as the value of "d."
In addition, in the conventional method of circuit configuration, the luminance and chrominance signals are separated and then the gamma compensation processing is individually performed with respect to each signal, so that four gamma compensation circuits (12d, 14b, 14c and 14d) become necessary. Accordingly, each gamma compensating circuit having non-linear characteristics should be embodied as a ROM look-up table, which consumes four such tables. Therefore, a significant amount of chip area is occupied in the form of IC processing, which has been a major obstacle in the reduction of chip size.